In 2013, WHO recommended that all HIV-infected women receive ART for PMTCT (PMTCT-ART). This approach provides treatment benefits for mothers and preventive benefits for their infants and sexual partners, and implementation advantages. However, there are valid concerns about risks of this approach if maternal retention or adherence falters. PMTCT programs have demonstrated remarkable flexibility to incorporate new HIV-specific counseling, testing and educational messages in maternal child health (MCH) clinics. PMTCT programs now need to add adherence and retention support for all women initiating lifelong ART in settings where health care workers are already overburdened. mHealth messaging is an evidence- based intervention that is attractive for this purpose. mHealth strategies have been shown to significantly decrease treatment failure in adult ART adult treatment programs in Africa and may provide an inexpensive, feasible approach to enhance PMTCT-ART outcomes without burdening health care workers. Our overarching hypothesis is that investment in mHealth for retention and adherence in PMTCT-ART will provide cost-effective benefit in sustaining antiretroviral regimen efficacy and durability. We have collaborated with the UW Department of Computer Sciences and Kenyan cell-phone providers to develop both inexpensive automated personalized SMS messaging and an innovative two-way SMS messaging system, currently in use MCH clinics in Kenya. In qualitative research, women in Kenya have expressed a strong desire for mHealth support to provide additional education, counseling and reminders to supplement counseling by health workers. We hypothesize that mHealth strategies will improve PMTCT-ART maternal and infant outcomes. We also posit that both one-way and two-way SMS approaches will be cost-effective, and that two-way SMS may be superior to one-way SMS. We propose a 3-arm randomized trial comparing one-way SMS vs, two-way SMS vs. control (no SMS) among HIV-infected Kenyan mothers in Kenyan PMTCT-ART programs. In AIM 1 we will compare trial arms for impact on maternal retention, adherence, virologic failure and resistance and infant HIV or HIV-free survival. In AIM 2, we will determine correlates of maternal loss to follow-up and virologic failur and correlates of infant HIV in the overall and stratified by trial arm. In the two-way SMS arm, we will determine rate of SMS interactivity, impact of critical time-points, and characteristics of high and low 'interactors'. In AIM 3, we will determine cost-effectiveness of one-way and two-way SMS interventions. These data will contribute a potential scale-able strategy to improve PMTCT-ART as programs aspire to 'virtual elimination' of infant HIV.